Ballast Resistor, do I have one?

[UncleWillie]

Re: Ballast Resistor, do I have one?

...the primary resistance in an ignition coil for a coil used on points is .9 of an ohm.
Please tell me the current draw at 12V, and then say 8V. All I want to know is the primary...
Electric motors are also inductive loads. How does ohms law apply to that?

12v / .9 ohms = ~13 amps. With a ~50% Dwell Angle. = ~6.5 Average.
Add a little Inductive reactance. = ~4 amps Average. A Typical Value.

That would be equivalent to .9 ohms Resistive, and .6 ohms Inductive Reactive.
The Resistance dominates in this circuit. (60%/40%)

But, If you simply attached this coil across a 12v battery with nothing else involved you will get the full 13 amps. A pure Resistive load, and Ohms law in it's basic form.
Don't leave the Key ON, with the engine not running, and the points closed!

I am NOT stating that there is NO Inductance in the Coil.
I am stating that it is far from a Black and White issue.

-------------------
In an AC Electric Motor/Transformer, Inductance will be expected to dominate.
Resistance will often account for well less than 10% of the Impedance.
If there were No Resistance, the Motors/Transformers would not heat up any at all.
AC Motors and Transformers vs. Ignition/Spark Coils is Apples and Oranges. :joyous:

 

[Maclin]

Re: Ballast Resistor, do I have one?

Thanks Uncle, Impedance is the term I was trying to come up with, total Resistance + Inductive. I used to have to do those graphs and calcs in an intern type position right out of tech school but it has been a (big, long) while

Ballast resistance is just that, in an inductive type circuit if keeps the volts from sloshing around. Well, sorta. Coil windings in a circuit always make life interesting.

 

[JustJason]

Re: Ballast Resistor, do I have one?

12v / .9 ohms = ~13 amps. With a ~50% Dwell Angle. = ~6.5 Average.
Add a little Inductive reactance. = ~4 amps Average. A Typical Value.

But on a running engine, an actual running engine. Your only going to see 1 to 1.5 amps if you actually measure it. Which is the point I'm trying to make. If you have an ammeter, and some time, and you can do this on anything that uses a 12v coil. But gap a set of plugs to .25, record your reading. And then gap a set to .60. And tell me if the current draw goes up, or stays the same. (for extra fun you can burn the contacts in the distro cap and file down the rotor a bit)